Materials Handbook 15th ed - G. Brady_ H. Clauser_ J. Vaccari (McGraw-Hill_ 2002) Episode 5 pot

They are noted for low gas and air permeability about 10times better than natural rubber, and for this reason they make agood material for tire inner tubes, hose, tubing, and diaphragms.

but may be colored by impurities to cream, gray, pink, green, orblack For furnace linings it is calcined, but for fluxing it is simplycrushed The raw dolomite, marketed by Basic Refractories, Inc.,for open-hearth steel making, is washed crushed stone in 0.625-in(1.6-cm) size When calcinated at a temperature of about 3100°F(1704°C), dolomite breaks down to MgO and CaO, and it is limited

to about 3000°F (1649°C) as a refractory Calcined dolomite used

in Germany as a water-filter material under the name of magno

masse is in grain sizes 0.02 to 0.2 in (0.5 to 5.0 mm) Dolomite for

the production of magnesia, some of which is cut as building ble, contains 10 to 20% magnesia, 27 to 33 lime, 1 to 12 alumina, 40

mar-to 46 carbonic acid, 1 mar-to 5 silica, and 0 mar-to 3 iron oxide The dolomitefound in huge deposits in Oklahoma contains 30.7% CaO, 21.3MgO, and only very small amounts of silica, alumina, and ironoxide For the production of magnesium metal, calcined dolomiteand ferrosilicon are brought to a high temperature in a vacuum,and the magnesium is driven off as a vapor In the ceramic indus-

try, dolomite is sometimes called bitter spar and rhombic spar.

Isostatic pressing and sintering a mixture of like amounts ofdolomite and synthesized zirconia plus 0.5% by weight lithium fluo-ride yields a ceramic having a melting point of 3722°F (2050°C) and

30 to 60% porosity that may be useful as a catalyst carrier for ing vehicle emissions Developed by the National Industrial ResearchInstitute of Nagoya in Japan, porosity is controlled by varying thesintering temperature between 1832 and 2552°F (1000 and 1400°C).Nanoceramics of this composition could be used for high-temperaturefilters

treat-DOUGLAS FIR. The wood of the tree Pseudotsuga taxifolia, of the

northwestern United States and British Columbia It is sometimes

called Oregon pine, Douglas pine, Douglas spruce, red fir, fir,

yellow fir, and Puget Sound pine The wood of young trees with wide

growth rings is reddish brown and is the type called red fir, though the true red fir is from the large tree Abies magnifica of California and

Oregon, the lumber of which is called golden fir, and the wood of which

is used also for paper pulp The wood of older trees of slower growth

with narrow rings is usually yellowish brown and is called yellow fir.

Both woods may come from the same tree The narrow-ringed wood isstronger and heavier Douglas fir averages below longleaf pine inweight, strength, and toughness, but above loblolly pine in strength andtoughness, though below it in weight The grain is even and close, withresinous pores less pronounced than in pitch pine It is a softwood and isfairly durable The density is 34 lb/ft3 (545 kg/m3) The compressivestrength perpendicular to the grain is 1,300 lb/in2(9 MPa); the shear-ing strength parallel to the grain is 810 lb/in2(5.5 MPa)

Douglas fir is used for general construction and millwork, plywood,boxes, flooring, and where large timbers are required It is also usedfor pulping and yields kraft paper of high folding endurance but lowbursting strength The fibers are large The trees grow to greatheights, the average being 80 to 100 ft (24 to 30 m) The stand is esti-mated at more than 450 billion bd ft (1 billion m3), or about one-fourth

of all timber in the United States Douglas fir bark contains from 7.6

to 18.3% of a catechol tannin, the bark of young trees yielding thehigher percentages It is suitable for tanning heavy leathers and

yields a pliable, light-colored leather Silvacon 383, of Weyerhaeuser

Co., is Douglas fir bark in flaky, corklike granules used in flooring

and acoustical tile Silvacon 490 is the bark as a reddish powder used in dusting powders and paints Silvacon 508 is hard, spindle-

shaped small fibers from the tissue of the bark, used as a filler for

plastics and in asphalt and fibrous paints Douglas-fir bark wax is

a hard, glossy wax extracted from the bark of the Douglas fir and is apartial replacement for carnauba wax A ton of bark yields 150 lb (68 kg) of wax by solvent extraction with 150 lb (68 kg) of tannin and

10 lb (4.5 kg) of quercetin as by-products

DRIERS. Materials used for increasing the rapidity of the drying ofpaints and varnishes The chief function of driers is to absorb oxygenfrom the air and transfer it to the oil, thus accelerating its drying to aflexible film They are in reality catalyzers Excessive use of drierswill destroy the toughness of the film and cause the paint to crack

Solutions of driers are called liquid driers; it is in this form that

paint driers are most used Certain oils, such as tung oil, have

inherent drying properties and are classified as drying oils but not asdriers Driers may be oxides of metals, but the most common driers

are metallic salts of organic acids Manganese acetate,

(CH3COO)2Mn 4H2O, is a common paint drier It is a pinkish, talline powder soluble in water and in alcohol and is used in

crys-strengths of 6, 9, or 12% metal Sugar of lead, used as a drier, is

lead acetate, Pb(CH3COO)2 3H2O, a white, cyrstalline powder with

a faint acetic acid odor, also used as a mordant in textile printing It

is known as plumbous acetate and Goulard’s powder Lead

oleate, Pb(C18H33O2)2, is a drier made by the action of a lead salt on

oleic acid It is used for thickening lubricants Lead linoleate,

Pb(C18H31O2)2, is a drier made by adding litharge to linseed oil andheating Lead and manganese compounds together act more effec-

tively as driers than either alone Lead resinate adds toughness of

film as well as drying power Because of antilead laws, this metal isbeing replaced by zinc, cobalt, calcium, and zirconium compounds

Zinar is a zinc resinate with 5.6% zinc content Cobalt octoate,

which has about 12% cobalt in combination with hexoic acid, is used

as a drier Cobalt driers are twice as rapid in drying power as

man-ganese driers, but too rapid drying often makes a wrinkled film which

is desirable for some finishes but not for others

Naphthenate driers are metallic salts made with naphthenic

acids instead of fatty-oil acids They are usually more soluble in paintsolvents, and since the naphthenic acids can be separated into a widerange of molecular weights by distillation, a wider variety of charac-

teristics can be obtained Sodium naphthenate, with 8.6% metal content, and potassium naphthenate, with 13.1%, are powders that are good bodying agents and emulsifiers as well as driers Tin naph-

thenate, with 20% tin, may be added to lubricating oils as an

antioxi-dant Mercuric naphthenate, with 29% mercury, retards the growth of bacteria and mold when added to finishes Barium naph-

thenate, with 22.6% barium, has binding and hardening properties

and is used in adhesives and in linoleum Uversols are naphthenic

acid salts of aluminum, calcium, cobalt, lead, manganese, or zinc, inliquid form for use as paint driers, wetting agents, and catalysts

Octoic driers, of Witco Corp., are metallic salts made with

ethylhex-oic acid, and the metal content is lower than that of driers made withnaphthenic acids They are light in color, have no odor, and have high

solubility The Octasols are ethylhexoic acid metal salts Drying

agents for resin coatings and inks may act by oxidation or other

chemical reaction Sulfur dichloride, S2Cl2, speeds the drying action

of coatings and inks formulated with alkyd, urea, or melamine resins,and such inks dry almost instantly

DRILL ROD. Tool-steel round rod made to a close degree of accuracy,generally not over or under 0.0005 in (0.0127 mm) the diameter size,and usually polished It is employed for making drills, taps, reamers,punches, or for dowel pins, shafts, and rollers Some mills also fur-nish square rods to the same accuracy under the name of drill rod.Common drill rod is of high-carbon steel hardened by quenching inwater or in oil The usual commercial sizes are from 1.5 in (3.8 cm) indiameter down to No 80, which is 0.0135 in (0.343 cm) in diameter.The usual lengths are 1 to 3 ft (0.3 to 0.9 m) The sizes are by thestandard of drill gages, with about 200 different diameters The car-bon content is usually from 0.90 to 1.05%, with 0.25 to 0.50 man-ganese, 0.10 to 0.50 silicon, and a maximum of 0.04 phosphorus orsulfur It also comes in high carbon with from 1.50 to 1.65% carbonand 0.15 to 0.35 manganese Drill rod can be obtained regularly in

high-speed steels and in special alloy steels for dowel pins Needle

wire is round tool-steel wire used for making needles, awls, and latch

pins It comes in coils, in diameters varying by gage sizes from 0.010

to 0.105 in (0.025 to 0.267 cm) Needle tubing for surgical

ments and radon implanters is stainless-steel tubing 0.014 to 0.203 in

(0.036 to 0.516 cm) in diameter in 6-ft (1.8-m) lengths Hypodermic

tubing is hard-drawn stainless-steel tubing 0.008 to 0.120 in (0.020

to 0.304 cm) in outside diameter, with wall thicknesses from 0.004 to0.012 in (0.010 to 0.304 cm), in 2-ft (0.6-m) lengths, with a fine finish

Capillary tubing is also stainless steel, but comes in lengths to

200 ft (61 m), with outside diameters from 0.060 to 0.125 in (0.152 to0.318 cm) The inside bore can be had in various diameters from 0.006

to 0.025 in (0.015 to 0.064 cm) for the 0.060-in (0.152-cm) tubing andfrom 0.010 to 0.024 in (0.025 to 0.061 cm) for the 0.125-in (0.318-cm)

tubing Stud steel is an English name for round bar steel made to

close limits and hardened and descaled, used for heavy pins and

studs Pin bar is small-diameter rod of case-hardened steel used for dowel pins Drill steel, for mine and quarry drills, comes in standard

rounds, octagons, squares, and cruciform bars, solid or hollow, usually

in carbon steel

DRYING OILS. Vegetable oils which are easily oxidized by exposure toair and thus suitable for producing a film in paints and varnishes,

known as paint oils The use of drying oils as the sole or main binder

in alkyd coatings is steadily decreasing with the advent of based latex paints Currently, it is limited to solvent-thinned exteriorhouse paints and some metal paints The oils are also used in oleo-resinous varnishes and in the manufacture of synthetic resins forcoating binders, epoxy ester resins, and oil-modified urethane resins.Small amounts are used in printing inks, linoleum, putty and caulk-ing compounds, core oils, and hardboard The best drying oils arethose which contain the higher proportions of unsaturated acids, inwhich oxidation causes polymerization of the molecules The drying of

water-an oleoresinous varnish takes place in two stages First, the reducer

or solvent evaporates, leaving a continuous film composed of gumsand drying oil The drying oil is then oxidized by exposure, leaving atough, hard skin This oxidation is hastened by driers, but the dryingoil itself is responsible for the film The drying power of oils is mea-

sured by their iodine value, as their power of absorbing oxygen from

the air is directly proportional to their power of absorbing iodine.Drying oils have typical iodine values about 140, semidry oils above

120, and nondrying oils are below 120 Linseed oil is the most mon of the drying oils, though tung oil and oiticica oil are faster indrying action Linseed oil alone will take about 7 days to dry, but can

com-be quickened to a few hours by the addition of driers Linseed oil andother oils may be altered chemically to increase the drying power

Conjugated oils are oils that have been altered catalytically by

nickel, platinum, palladium, or carbon to give conjugated double

bonds in place of isolated double bonds in the molecules of the fatty

acids Conjulinol is a drying oil of this class made from linseed oil.

The iodine value is 180, and the drying time is greatly reduced.Normally, soybean oil is not classed as a drying oil although it may beblended with drying oils for paint use But by chemical alterationand, lately, by mixing with synthetic resins, it can be given good dry-

ing power Conjusoy is a drying oil made by conjugation of soybean

oil The iodine value is 128, and the drying time is about half that ofboiled linseed oil

Castor oil, which has poor drying properties, is dehydrated to form

a good drying oil Other methods are used to alter oils to increase thedrying power, notably polymerization of the linoleic and some otheracids in the oils; or oils may be fractionated and reblended to increase

the percentage of acids that produce drying qualities The Admerols,

of the Archer-Daniels-Midland Co., comprise a series of drying oilsmade by treating linseed or soybean oil with butadiene, styrene, or

pentaerythritol Kel-X-L oil, of Spencer-Kellogg, is a modified linseed

oil with an iodine value up to 170, used as a substitute for tung oil in

quick-drying varnishes Kellin, of the same company, is a quick-drying blended oil with a linseed-oil base, while Kellsoy is a similar oil with a soybean-oil base Cykelin, of the same company, is a quick-drying oil made by treating linseed oil with cyclopentadiene, (CH:CH)2 CH2, alow-boiling liquid obtained from coal tar or from cracking petroleum

Cykelsoy is another drying oil made by treating soybean oil with

cyclopentadiene Dorscolene is a drying oil made from fractionated

and blended fish oils The German substitute drying oil known as

Resinol was a liquid obtained by the distillation of the heavy

frac-tions of the benzolated oils derived from scrubbing coke-oven gas

Resigum is the final residue in the distillation of tar-oil benzol which

has been washed with sulfuric acid, caustic soda, and water It tains a maximum naphthalene content of 5% It is miscible withresins or copals, and with vegetable oils, and makes a good paint

con-without other drying oils Synthetic drying oil is glycerol allyl ether derived from propylene gas obtained in cracking petroleum C oil is a

heavy, sticky liquid with a butadiene base In paints it gives highadhesion to metals and masonry and produces a smooth, hard, glossycoating with good chemical resistance

Although the great volume of drying oils is produced from linseed,soybean, tung, oiticica, castor, and fish oils, many other oils have dry-

ing properties and are used in varying quantities N’gart oil is from

the seed nuts of a climbing plant of Africa and is equal in drying

power to linseed oil Lallemantia oil, obtained from the seeds of

Lallemantia iberica, of southeastern Europe and Asia, resembles

lin-seed oil in physical properties Isano oil, obtained from the kernel of

the nut of Ongokea klaineana of tropical Africa, is a pale-yellow

vis-cous oil that has little drying power, but when heat-treated sets up an

exothermic action to produce a varnish oil Anda-assu oil, also used

in Brazil for paints, is from the seeds of the plant Joannesia princeps.

The seeds yield 22% of a clear yellow oil with an iodine value of 142

which is bodied by heating Manketti oil is a varnish oil with about

two-thirds the drying power of linseed oil It is a light-yellow viscous

oil from the seed nuts of the tree Ricinodendron rautanenii, of

south-west Africa

Chia-seed oil is a clear amber-colored oil extracted from the seeds

of the plant Salvia hispanica of Mexico It has a higher drying value

than linseed oil The seeds yield about 30% oil, which contains 39%linolenic acid, 45 linoleic, 5 palmitic, 2.7 stearic, with some arachidic,oleic, and myristic acids The specific gravity is 0.936, iodine value

192, and acid value 1.4 The seeds scatter easily from the pods andare difficult to collect

DUCK. A strong, heavy cotton fabric employed for sails, awnings,tents, heavy bags, shoe uppers, machine coverings, and where aheavy and durable fabric is needed It is woven plain, but with twothreads together in the warp It is made in various weights and isdesignated by the weight in ounces per running yard 22 in (0.6 m)wide It is marketed unbleached, bleached, or dyed in colors, andthere are about 30 specific types with name designations usually for

particular uses such as sailcloth When woven with a colored stripe,

it is called awning duck Russian duck is a fine variety of linen

duck Large quantities of cotton duck are used for making

lami-nated plastics and for plastic-coated fabrics, and it is then simply

designated by the weight Belt duck, for impregnated conveyor

and transmission belts, is made in loosely woven, soft ducks and inhard-woven, fine-yarn hard fabric The weights run from 28 to 36 oz

(0.80 to 1.02 kg) Conveyor belting for foodstuff plants is usually

of plastic fabric for cleanliness Transilon, of Extremultus, Inc., is

a belting of good strength and flexibility to operate over diameter rollers It is made of nylon fabric faced on both sides withpolyvinyl chloride sheet It may have a variety of surface finishessuch as tetrafluoroethylene

small-Hose duck, for rubber hose, is a soft-woven fabric of plied yarns not

finer than No 8, made in weights from 10 to 24 oz (0.28 to 0.68 kg)

The grade of duck known as elevator duck for conveyor belts is a hard-woven 36-oz (1.02-kg) fabric Plied-yarn duck is used for army

tents instead of flat duck as it does not tear easily and does not require

sizing before weaving Canvas is duck of more open weave The term

is used loosely in the United States to designate heavy duck used for

tarpaulins, bags, sails, and tents But more properly it is a heavy duck

of square mesh weave more permeable than ordinary duck, such as the

canvas used for paintings and for embroidery work The word duck is from the Flemish doeck, meaning cloth, originally a heavy linen fabric The word canvas is from the Latin cannabis, originally a coarse, heavy

hempen cloth for tents Osnaburg cloth is a heavy, coarse,

plain-woven fabric used for wrapping and bailing and for inside sacks forburlap flour bags It is made from lower grades of short-staple cottonand from waste In colored checks and stripes it is used for awnings

Drill is a stout, twilled cotton fabric used for linings and where a

strong fabric lighter than duck is required It differs from duck also inthat it has a warp-flush weave that brings more warp than filling tothe face of the cloth It comes unbleached, bleached, or piece-dyed, or

it may be yarn-dyed It is made in various weights and is designated

in ounces per yard, the same as duck Tan-colored drill is called

khaki Denim is a heavy, twill-woven, warp-flush fabric usually

lighter in weight than drill The warp is yarn-dyed The filling ismade with one black and one white yarn It is much used for workers’

clothing, and the light weights for sportswear are called jean Denim

is also used industrially where a tough fabric is needed Art denim,

in plain colors or woven with small figures, is used for upholstery

DYESTUFFS Materials, also called colorants, used to color textiles,

paper, leather, wood, or other products They may be either natural orartificial Many chemicals will stain and color other materials, but aproduct is not considered a dye unless it will impart a distinct color ofsome permanence to textiles The natural dyestuffs may be mineral,animal, or vegetable, but the artificial dyes are derived mainly fromcoal-tar bases Almost all naturally extracted dyes have been replaced

by synthetic counterparts for commercial use; an exception is

log-wood, a Central American tree extract, known as natural black 1,

CI 75290 Tyrian purple, from various Mediterranean snails, was in

ancient times the most noted of the animal dyestuffs Cochineal and

kermes are other animal dyes One of the earliest metallic or mineral

dyestuffs was called iron buff It was made by allowing pieces of iron

to stand in a solution of vinegar to corrode Fabrics that had beendipped in this solution were rinsed in a solution of wood ashes

Mineral dyes now include ocher, chrome yellow, and Prussian blue Vegetable dyes may be water solutions of woods, barks, leaves,

fruits, or flowers The buff and brown textile colors of early NewEngland were made by boiling fresh green butternuts in water, while

a dark-red dye was made by boiling the common red beet in water

The yellow to red colors known by the Algonquin name of puccoon were from the orange-red juice of the root of the bloodroot, a peren-

nial of the poppy family Vegetable dyes now include brazilwood, wood, sappanwood, fustic, logwood, madder, henna, saffron, annatto,

bar-indigo, and alkanet The camphire of the ancients mentioned in the

Bible and Koran was a reddish-orange dyestuff made by grinding to apaste the red, sweet-scented spikes of the small cypress tree

Lawsonia inermis, of Egypt and the Near East It was used by

Eastern and Roman women to stain fingernails, and is now used

under the name henna for dyeing leather and hair It gives various shades from yellowish to red or brown Argol, a brilliant red used extensively until replaced by synthetic dyes, is from the orchilla, a

lichen found in the Canaries and Near East It was used to produce

the brilliant colors of the medieval Florentine cloth Chinese

green, buckthorn bark, or lokao is the powdered bark of the

buck-thorns, Rhamorus globosa and R utilis, of China and Russia It is

used in dyeing silk and cotton Weld, from the plant Reseda luteola of

Europe, produces a very bright-yellow color with an alum mordant

With indigo it produces green Woad is the dried fermented leaves of

the plant Isatis tinctoria of Europe It gives a blue color, but is now

little cultivated Ecolor dyes, of Allegro Natural Dyes, are derived

from plants, such as the Maclura pomifera (Bodark tree) and the

insect, cochineal No heavy metals are required as mordants to treat fibers to accept the dyes, and no toxics or solvents, other thanwater, are used in dyeing More than 100 colors exist for cotton fibers.Synthetic dyes are mostly coal-tar or aniline colors They are moreintense, brighter, faster, and generally cheaper than natural dyestuffs.The dyes are complex chemicals, but they usually contain characteris-tic groups of atoms so that the color or change in color can be pre-dicted The Colour Index (CI) from the U.K.’s Society of Dyers andColourists is a new system for classifying dyes It assigns a numberdefining the chemical class while a generic name identifies the appli-

pre-cation; in industry, the trade name is also appended

Benzene-azo-m-phenylenediamine hydrochloride is sold as Chrysoidine Y and

classified as Azo or Basic Dye, CI 11270, Basic Orange 2 The

Colour Index recognizes 26 types of dyes by chemical classification

The azo dyes, with an  N:N  linkage, constitute about half of theproduction and are produced by diazotization of primary arylamines,followed by reaction with aromatic amines, phenols, and enolizable

ketones Azobenzene, C6H5 N:N  H5C6, is made from nitrobenzeneand is in crystalline red plates melting at 154°F (68°C) This may be

converted to hydrazobenzene, C6H5NHNHC6H5, a solid of

camphor-like odor melting at 268°F (131°C) Substituted azo dyes constitute

a class containing OH and NH groups, made by coupling amines orphenols with the salts The azo dyes are in general poisonous, but aresometimes used in restricted quantities to color foodstuffs Some are

poisonous in contact with skin, such as xylyazonaphthol and the sodium salt of sulfophenylazo, designated by the Food and Drug Administration as red No 32 and orange No 1, and proscribed for

use in coloring lipstick and oranges

Three other important classes are anthraquinone dyes, indigoid

dyes, and thioindigoid dyes, the latter being sulfur dyes The

sul-fur dyes may be made by treating the organic compounds withsodium sulfide They are fast to washing and to light, but the range ofcolor is limited, and their use is generally limited to fibers where astrongly alkaline bath is tolerable

Some of the synthetic dyes will color animal fibers well and not etable fibers, or vice versa, while some will color all fibers As a result,

veg-it is possible to divide the bulk of the dyes into six classes, including

azoic dyes The direct dyes can be dyed directly, while others

require a mordant Some are permanent, or fast, while others arewater-soluble and will fade when the fabric is washed, or some maynot be light-fast and will fade when exposed to light Direct dyes usu-ally have a weak OH bond between the nitrogen in the dye and the

fiber, usually cotton In reactive dyes, the dye reacts with the fiber to

produce both an OH and an oxygen linkage, the chlorine combiningwith the hydroxyl to form a strong ether linkage Such dyes are fast

and very brilliant and are used for cotton, rayon, and nylon Acid

dyes contain a carboxylic or sulfonic acid group and operate best in an

acid bath They are used for drying protein fibers, such as wool, silk,and nylon, and sometimes for leather and paper They are usually azo,

triaryl methane, or anthroquinone complexes Basic dyes are

com-monly amino and substituted amino compounds, such as triaryl

methane or xanthenes They are used for dyeing cotton with a dant Vat dyes are insoluble and are applied in the soluble colorless

mor-form and then reduced or oxidized to color They usually have an

anthraquinone or indanthrene structure and are solubilized by the

reducing agent, a hydroxyl group, OH, diffusing into the fiber where it

is fixed The best known example is indigo, the dye synonymous with

the color of bluejeans, which has become one of the most important

colorants because of the popularity of denim garments Originally

derived from plants, synthetic indigo dye now dominates the market.Synthesis, first commercialized by BASF of Germany more than 100years ago, uses aniline formaldehyde and sodium cyanide as the rawmaterials The process generates toxic wastewater A biosynthesisprocess, of Genecor International, Inc., however, is said to be environ-mentally benign Pioneered by Amgen, Inc., and the University ofTexas, it uses no petrochemical feedstocks, and biomass is the only

waste product Genecor produces recombinant Escherichia coli

bacte-ria, which contain an enzyme capable of converting indole to indigo.

Indole is a naturally occurring by-product of an enzyme within E coli.

Bifunctional reactive dyes, such as the Sumifix Supra line of

Sumitomo, of Japan, combine several reactive groups in a single ecule Each group compensates for the other during changing process

mol-conditions, improving color fixation and reproducibility The Levafix

line, of Miles Inc., combines vinyl sulfone, monofluorotriazine, andfluorochloropyrimidine to increase color fixation rates to 75 to 90% andhigher in contrast with the 50 to 70% rates typical of conventional reac-

tive dyes Cibacron C bifunctional reactives, of Ciba Geigy, are said to

provide color fixation rates of 95% Increasing the fixation rate reducesthe amount of dye discharged in textile wastewater To reduce sulfur

effluents in nonreactive sulfur dyes, Sandozol RDT, of Sandoz

Chemical Corp., contains nonsulfide-reducing agents, which cut sulfideconsumption in half

Color carriers, used to aid adherence of dyes to synthetic fibers,

are usually chemicals that act as swelling agents to open the fiberstructure, such as phenylphenol, benzoic acid, or dichlorobenzoic acid

Ketosol 75, of Union Carbide, is 75% methylphenyl carbinol and 25

acetophenone Monochlorobenzene, used as a color carrier for Dacronfiber, acts to promote a concentrated layer of dye solution around the

fiber Ring-dyed fiber is a synthetic fiber not receptive to dyes that

has been passed through a bath of a receptive plastic before dyeing.The dye then adheres to the coated surface and encases the fiber

EBONY. A hard, black wood valued for parts subject to great wear,and for ornamental inlaying It is the wood of various species of trees

of the ebony family, Ebenaceae, although the name is also applied to

some woods of the genus Dalbergia, family Leguminosae Black

ebony, from the tree Diospyros dendo of West Africa, and ebony, from

the tree D melanoxylos, of India, are the true ebonies Black ebony

has a black heartwood with brownish-white sapwood It is next tolignum vitae in hardness and has a fine, open grain and a density of

78 lb/ft3(1,250 kg/m3) It is used for inlaying, piano keys, and turnery.The ebony of India is also extremely hard, with a fine, even grain The

heartwood is black with brownish streaks Marblewood, or

Andaman marblewood, is an ebony from the tree D kurzii of India

and the Andaman Islands The wood is black with yellowish stripes Ithas a close, firm texture, is hard, takes a fine polish, and has a density

of 65 lb/ft3 (1,041 kg/m3) Marble ebony is another species from

Malagasy The ebony from Japan, called kaki, is from the tree D kaki.

It has a black color streaked with gray, yellow, and brown The grain isclose and even, and the wood is very hard, but the density is less thanthat of African ebony Ebony wood is shipped in short billets and isgraded according to the color and the source, as Niger, Macassar, or

Cameroon Green ebony is a name sometimes given to the cocoswood

of the West Indies Artificial ebony, formerly composed of asphaltic

compounds, is now usually molded plastics Partridgewood, a heavy blackish wood used for fine inlay work, is acapau, from the large tree

Voucapapoua americana of the Amazon Valley It is valued in Brazil

for furniture because of its resistance to insect attack

ELASTOMERS Synthetic rubbers, often referred to as rubbers,

are hydrocarbon polymeric materials similar in structure to plasticresins The difference between plastics and elastomers is largely one

of definition based on the property of extensibility, or stretching The

American Society for Testing and Materials defines an elastomer as “a

polymeric material which at room temperature can be stretched to atleast twice its original length and upon immediate release of thestress will return quickly to approximately its original length.” Somegrades of plastics approach this rubberlike state, for example, certain

of the polyethylenes Also, a number of plastics have elastomergrades, such as the olefins, styrenes, fluoroplastics, and silicones Asindicated above, the major distinguishing characteristic of elastomers

is their great extensibility and high-energy storing capacity Unlikemany metals, for example, which cannot be strained more than afraction of 1% without exceeding their elastic limit, elastomers haveusable elongations up to several hundred percent Also, because oftheir capacity for storing energy, even after they are strained severalhundred percent, virtually complete recovery is achieved once thestress is removed

Up until World War II, almost all rubber was natural During the

war, synthetic rubbers began to replace the scarce natural rubber,

and since that time, production of synthetics has increased until nowtheir use far surpasses that of natural rubber There are thousands ofdifferent elastomer compounds Not only are there many differentclasses of elastomers, but also individual types can be modified with avariety of additives, fillers, and reinforcements In addition, curingtemperatures, pressures, and processing methods can be varied toproduce elastomers tailored to the needs of specific applications

In the raw-material or crude stage, elastomers are thermoplastic

Thus crude rubber has little resiliency and practically no strength.

By a vulcanization process in which sulfur and/or other additives areadded to the heated crude rubber, the polymers are cross-linked bymeans of covalent bonds to one another, producing a thermosetlikematerial The amount of cross-linking which occurs between the sul-fur (or other additive) and the carbon atoms determines many of theelastomer’s properties As cross-linking increases, resistance to slip-page of the polymers over one another increases, resiliency and exten-sibility decrease, and the elastomer approaches the nature of athermosetting plastic For example, hard rubbers, which have the

highest cross-linking of the elastomers, in many respects are similar

to phenolics In the unstretched state, elastomers are essentiallyamorphous because the polymers are randomly entangled and there

is no special preferred geometric pattern present However, whenstretched, the polymer chains tend to straighten and become aligned,thus increasing in crystallinity This tendency to crystallize whenstretched is related to an elastomer’s strength Thus, as crystallinityincreases, strength also tends to increase

There are roughly 20 major classes of elastomers; we cannot domuch more here than identify them and highlight the major charac-teristics of each group Two basic specifications provide a standardnomenclature and classification system for these classes The ASTMstandard D1418 categorizes elastomers into compositional classes

A joint ASTM-SAE specification (ASTM D2000/SAE J200) provides

a classification system based on material properties The first letterindicates specific resistance to heat aging, and the second letterdenotes resistance to swelling in oil

Styrene-butadiene elastomers, sometimes also called Buna S, SBR, and GR-S, are copolymers of butadiene and styrene They are sim-

ilar in many ways to the natural rubbers, and were the first widely usedsynthetics They top all elastomers in volume of use, chiefly because oftheir low cost and use in auto tires A wide range of property grades areproduced by varying the relative amounts of styrene and butadiene Forexample, styrene content varies from as low as 9% in low-temperatureresistant rubbers to 44% in rubbers with excellent flow characteristics.Those grades with styrene content above 50% are by definition consideredplastics Carbon black is sometimes added also as it substantiallyimproves processing and abrasion resistance SBR elastomers are similar

in properties to natural rubber They are non-oil-resistant and are ally poor in chemical resistance Although they have excellent impact andabrasion resistance, they are somewhat below natural rubber in tensilestrength, resilience, hysteresis, and some other mechanical properties.The largest single use is in tires Other applications are similar to those of

gener-natural rubber Styrene-butadiene latex, typically a 70% SBR sion in water, is used mainly for coatings and adhesives Carbon tetra-

emul-chloride, CCl4, long used as a weight modifier in some of the latex, isbeing phased out for environmental reasons Japan SyntheticRubber, that country’s largest producer of latex, has developed a non-halogen hydrocarbon-based substitute for all latex grades formerlyusing CCl4 New solution polymers of Goodyear Chemical Co., based

on styrene-isoprene-butadiene rubber, improve wet traction of tires over standard emulsion SBR This is also true of Li polymers,

so called because of the lithium-based catalyst used during ization in hexane or other organic solvent

Neoprene, also known as chloroprene, was developed in the

1930s, and it has the distinction of being the first commercial thetic rubber It is chemically and structurally similar to natural rub-ber, and its mechanical properties are also similar Its resistance tooils, chemicals, sunlight, weathering, aging, and ozone is outstanding.Also, it retains its properties at temperatures up to 250°F (121°C),and it is one of the few elastomers that does not support combustion,although it is consumed by fire In addition, it has excellent resis-tance to permeability by gases, having about one-fourth to one-tenththe permeability of natural rubber, depending on the gas Although it

syn-is slightly inferior to natural rubber in most mechanical properties,neoprene has superior resistance to compression set, particularly atelevated temperatures It can be used for low-voltage insulation, but isrelatively low in dielectric strength Typical products made of chloro-prene elastomers are heavy-duty conveyor belts, V belts, hose covers,

footwear, brake diaphragms, motor mounts, rolls, and gaskets Butyl

rubbers, also referred to as isobutylene-isoprene elastomers, are

copolymers of isobutylene and about 1 to 3% isoprene They are lar in many ways to natural rubber and are one of the lowest-pricedsynthetics They have excellent resistance to abrasion, tearing, andflexing They are noted for low gas and air permeability (about 10times better than natural rubber), and for this reason they make agood material for tire inner tubes, hose, tubing, and diaphragms.Although butyls are non-oil-resistant, they have excellent resistance

simi-to sunlight and weathering and generally have good chemical tance They also have good low-temperature flexibility and heatresistance up to around 300°F (149°C); however, they are not flame-resistant They generally have lower mechanical properties, such astensile strength, resilience, abrasion resistance, and compression set,than the other elastomers Because of their excellent dielectricstrength, they are widely used for cable insulation, encapsulatingcompounds, and a variety of electrical applications Other typicaluses include weather stripping, coated fabrics, curtain wall gaskets,high-pressure steam hoses, machinery mounts, and seals for foodjars and medicine bottles

resis-Isoprene is synthetic natural rubber It is processed as natural

rubber, and its properties are quite similar, although isoprene hassomewhat higher extensibility Like natural rubber, its notable charac-teristics are very low hysteresis, low heat buildup, and high tear resis-tance It also has excellent flow characteristics and is easilyinjection-molded Its uses complement those of natural rubber And itsgood electrical properties plus low moisture absorption make it suitable for

electrical insulation Polyacrylate elastomers are based on polymers of

butyl or ethyl acrylate They are low-volume-use, specialty elastomers,

chiefly used in parts involving oils (especially sulfur-bearing) at elevatedtemperatures up to 300°F (149°C) and even as high as 400°F (204°C) Amajor use is for automobile transmission seals Other oil-resistantuses are gaskets and O rings Mechanical properties such as tensilestrength and resilience are low And, except for recent new formula-tions, they lose much of their flexibility below 10°F (23°C) Thenew grades extend low-temperature service to 40°F (40°C).Polyacrylates have only fair dielectric strength, which improves,however, at elevated temperatures.

Nitrile elastomers, or NBR rubbers, known originally as Buna N,

are copolymers of acrylonitrile and butadiene They are principallyknown for their outstanding resistance to oil and fuels at both normaland elevated temperatures Their properties can be altered by varyingthe ratio of the two monomers In general, as the acrylonitrile contentincreases, oil resistance, tensile strength, and processability improvewhile resilience, compression set, low-temperature flexibility, and hys-teresis characteristics deteriorate Most commercial grades rangefrom 20 to 50% acrylonitrile Those at the high end of the range areused where maximum resistance to fuels and oils is required, such as

in oil-well parts and fuel hose Low-acrylonitrile grades are usedwhere good flexibility at low temperatures is of primary importance.Medium-range types, which are the most widely used, find applica-tions between these extremes Typical products are flexible couplings,printing blankets, rubber rollers, and washing-machine parts.Nitriles as a group are low in most mechanical properties Becausethey do not crystallize appreciably when stretched, their tensilestrength is low, and resilience is roughly one-third to one-half that ofnatural rubber Depending on acrylonitrile content, low-temperaturebrittleness occurs at from 15 to 75°F (26 to 60°C) Their electri-cal insulation quality varies from fair to poor

Hydrogenated nitrile rubber, of Bayer AG of Germany, has good

heat stability, abrasion resistance, and dynamic-load capacity It is used

for synchronous belts in auto applications Zeptol elastomers, of Zeon Chemicals, Inc., are hydrogenated nitrile-butadiene rubbers for ser-

vice temperatures of 30 to 302°F (1 to 150°C) They have good tensile

strength and resistance to lubricants Phosphonitrile elastomers

have high elasticity and high-temperature resistance They are derived

from chlorophosphonitrile, or phosphonitrilic chloride, P3N3Cl3,which has a hexagonal ring of alternating atoms of phosphorus and

nitrogen with chlorine atoms attached (In phosphonitrile plastics,

the chlorine atoms are replaced by other groups.)

Polybutadiene elastomers are notable for their low-temperature

performance With the exception of silicone, they have the lowest brittle

or glass transition temperature, 100°F (73°C), of all the tomers They are also one of the most resilient, and have excellentabrasion resistance However, resistance to chemicals, sunlight,weathering, and permeability by gases is poor Some uses are shoeheels, soles, gaskets, and belting They are also often used in blendswith other rubbers to provide improvements in resilience, abrasionresistance, and low-temperature flexibility.

elas-Polysulfide elastomer is rated highest in resistance to oil and

gasoline It also has excellent solvent resistance, extremely low gaspermeability, and good aging characteristics Thus, it is used for suchproducts as oil and gasoline hoses, gaskets, washers, anddiaphragms Its major use is for equipment and parts in the coatingproduction and application field It is also widely applied in liquidform in sealants for the aircraft and marine industries Its mechani-cal properties, including strength, compression set, and resilience, arepoor Although it is poor in flame resistance, it can be used in temper-

atures up to 250°F (121°C) Ethylene-propylene elastomers, or

EPR rubber, are available as copolymers and terpolymers They

offer good resilience, flexing characteristics, compression-set tance, and hysteresis resistance, along with excellent resistance toweathering, oxidation, and sunlight Although they are fair to poor inoil resistance, their resistance to chemicals is good Their maximumcontinuous service temperature is around 350°F (177°C) Typicalapplications are electrical insulation, footwear, auto hose, and belts

resis-The terpolymer, ethylene propylene diene monomer (EPDM), has

recently been produced with metallocene and other single-site lysts used in polyethylene and polypropylene production

cata-Urethane elastomers are copolymers of diisocyanate with

poly-ester or polyether Both are produced in solid gum form and viscousliquid With tensile strengths above 5,000 lb/in2 (34 MPa) and somegrades approaching 7,000 lb/in2(48 MPa), urethanes are the strongestavailable elastomers They are also the hardest, and have extremelygood abrasion resistance Other notable properties are low compres-sion set, and good aging characteristics and oil and fuel resistance.The maximum temperature for continuous use is under 200°F (93°C),and their brittle point ranges from 60 to 90°F (51 to 68°C).Their largest field of application is for parts requiring high wear resis-tance and/or strength Typical products are forklift truck wheels, air-plane tail wheels, shoe heels, bumpers on earth-moving machinery,typewriter damping pads, seals and flexible linings for sewage-treatmentand chemical-storage tanks For seal applications, maximum recom-mended deflection limits are 50% for Shore A hardness 40 to 60, 30% for

70, 20% for 80, 10% for 95, and 5% for Shore D 70

Sorbothane is a polyether urethane from Sorbothane Inc., in

Shore 00 hardness 25 to 80 Intended for shock, vibration, and noisecontrol, it is used for stud mounts, grommets, bushings, pads, andother isolation-damping products At Shore 50, the specific gravity is1.3, density 0.047 lb/in3(1300 kg/m3), tensile strength 125 lb/in2(0.86MPa), tear strength 23.5 lb/in2 (0.16 MPa), and compression set

6.2% Master Bond Inc.’s UV15X-5 urethane is a one-component,

nonyellowing, ultraviolet-curing, transparent elastomer of excellentflexibility and abrasion resistance for bonding to metals, plastics,elastomers, and glass and for sealing, coating, or casting Totallyreactive, it emits no volatiles on curing and has a service tempera-ture range of 80 to 250°F (62 to 121°C) Shore D hardnessexceeds 30 and the tensile strength is 1800 lb/in2 (12.4 MPa)

Isoloss is a series of specially formulated urethanes, of E-A-R

Specialty Composites Div of Cabot Safety Corp., for damping noise,vibration, and shock

Polyethylene elastomers are rubberlike materials made by

cross-linking with chlorine and sulfur, or they are ethylene

copoly-mers Chlorosulfonated polyethylene elastomer, commonly known as Hypalon, contains about one-third chlorine and 1 to 2%

sulfur It can be used by itself or blended with other elastomers It isnoted for its excellent resistance to oxidation, sunlight, weathering,ozone, and many chemicals Some grades are satisfactory for con-tinuous service at temperatures up to 350°F (177°C) It has moder-ate oil resistance It also has unlimited colorability Its mechanicalproperties are good but not outstanding, although abrasion resis-tance is excellent Hypalon is frequently used in blends to improveoxidation and ozone resistance Typical uses are tank linings, high-temperature conveyor belts, shoe soles and heels, seals, gaskets,and spark plug boots

Ethylene-propylene elastomer, produced by various companies,

is a chemically resistant rubber of high tear strength Ethylene

butadiene can be vulcanized with sulfur to give high hardness and

wide temperature range For greater elongation a terpolymer with

butene can be made Epichlorohydrin elastomers are noted for

their good resistance to oils and excellent resistance to ozone, ering, and intermediate heat The homopolymer has extremely lowpermeability to gases The copolymer has excellent resilience at lowtemperatures Both have low heat buildup, making them attractivefor parts subjected to repeated shocks and vibrations

weath-Fluorocarbon elastomers, like their plastic counterparts, excel in

resistance to oxidation, chemicals, oils, solvents, and heat They are alsoquite costly Many have continuous-use service temperatures as high as

400°F (204°C), some can withstand higher temperatures, and they willnot support combustion Most are brittle, however, at 10°F (23°C),

and their mechanical properties are only moderate Viton, of Du Pont

Dow, comes in families designated A, B, F, and ETP Viton A’s are mers of vinylidene fluoride (VF2) and hexafluoropropylene (HFP) TheB’s and F’s are terpolymers of VF2, HFP, and tetraflurorethylene (TFE).ETPs are peroxide-cured terpolymers of ethylene, TFE, and perfluo-romethylvinylether (PMVE) with a small amount of cure-site monomer

dipoly-to permit peroxide cross-linking Resistance dipoly-to fluids generally rises withincreasing fluorine content—66% in Type A, 67 in ETP, 68 in B, and 70

in F—but low-temperature flexibility tends to decline with that increase

3M’s Fluorel elastomers, with 65 to 71% fluorine, are either

dipoly-mers of VF2and HFP or terpolymers of VF2, HFP, and TFE Depending

on the grade, their density is 0.065 to 0.069 lb/in3(1799 to 1910 kg/m3),tensile strength 1,460 to 2,560 lb/in2 (10 to 18 MPa), elongation 180 to330%, Shore A hardness 70 to 84, compression set for 70 h at 392°F(200°C) 9 to 45%, and the continuous-use temperature 0 to 392°F (17.8

to 200°C) The properties of Fluorel II, a VF2-TFE-propylene elastomer,are within these ranges except for density [0.058 lb/in3(1605 kg/m3)]

Aflas, a 3M dipolymer of TFE and propylene with 57% fluorine, has a

density of 0.056 lb/in3 (1550 kg/m3) and a service temperature range

of 35 to 392°F (2 to 200°C) Depending on the grade, tensile strength

is 1,690 to 2,440 lb/in2 (11.7 to 17 MPa), elongation 220 to 325%,Shore A hardness 72 to 73, and compression set for 70 h at 392°F(200°C) of 42 to 50% Except for its higher low-temperature servicetemperature and the greater acid resistance of peroxide-curedFluorel, the overall environmental resistance of Alfas is superior to

that of Fluorel and Fluorel II A phosphonitrilic fluorocarbon

elastomer, developed by Firestone Tire and Rubber Co., retains

flexi-bility at temperatures as low as 70°F (57°C), sustains tures as high as 350°F (177°C), and is especially resistant to oils and

tempera-solvents over this temperature range Kalrez

perfluorocarbonelas-tomer, of Du Pont Dow, has the highest continuous-use service

tem-perature of any fluorocarbon elastomer: 550°F (288°C) This mostcostly of elastomers can withstand short-term temperatures to 650°F(343°C) and is also resistant to a variety of solvents, bases, and fuels

Chlorinated polyethylene elastomers are produced by

substitution of chlorine for hydrogen on a high-density ene chain, resulting in a fully saturated structure with no double

polyethyl-or triple bonds The elastomer requires the catalytic reaction of aperoxide for curing Thus, most molded parts are black Five

grades of CPE polymers are produced, differing principally in

chlorine content The higher-chlorine-content grades have best oiland fuel resistance, tear resistance, gas impermeability, and hard-

ness Those with lower chlorine content have lower viscosities, betterlow-temperature properties, and improved resistance to heat and com-pression set.

Silicone elastomers are polymers composed basically of silicone and

oxygen atoms There are four major elastomer composition groups Interms of application, silicone elastomers can be divided roughly into thefollowing types: general-purpose, low-temperature, high-temperture, low-compression-set, high-tensile–high-tear, fluid-resistant, androom-temperature vulcanizing All silicone elastomers are high-performance, high-price materials The general-purposegrades, however, are competitive with some of the other specialtyrubbers and are less costly than the fluorocarbon elastomers Siliconelastomers are the most stable group of all the elastomers They areoutstanding in resistance to high and low temperatures, oils, and chemi-cals High-temperature grades have maximum continuous service tem-peratures up to 600°F (316°C); low-temperature grades have glasstransition temperatures of 180°F (118°C) Electrical properties, whichare comparable to the best of the other elastomers, are maintained over atemperature range from 100°F (73°C) to over 500°F (260°C) However,most grades have relatively poor mechanical properties Tensile strengthruns only around 1,200 lb/in2(8 MPa) However, grades have been devel-oped with much improved strength, tear resistance, and compression set

Liquid silicone elastomers are more costly than conventional solid

silicones, especially in terms of mold cost, because of the greater sion required Production cost may be less, however, because of muchfaster cure time Molding, at temperatures of 250 to 400°F (121 to204°C), is performed in injection-molding machines similar to those forinjection-molding plastics Applications include gaskets integrallymolded onto their respective plastic or metal component, spark plug

preci-covers, bellows, and various seals Fluorosilicone elastomers have

been developed which combine the outstanding characteristics of the rocarbons and silicones However, they are expensive and require specialprecautions during processing A unique characteristic of one of theseelastomers is its relatively uniform modulus of elasticity over a wide tem-perature range and under a variety of conditions Silicone elastomers areused extensively in products and components where high performance isrequired Typical uses are seals, gaskets, O rings, insulation for wire andcable, and encapsulation of electronic components

fluo-ELECTRICAL-CONTACT MATERIALS. These are materials used to makeand break electrical contact, thus make-and-break electric circuits, or toprovide sliding or constant contact Both require high electrical conduc-tivity to ease current flow, high thermal conductivity to dissipate heat,high melting point or range to inhibit arc erosion and prevent sticking,

corrosion and oxidation resistance to prevent formation of films thatimpede current flow, high hardness for wear resistance, and amenability

to welding, brazing, or other means of joining The sliding-contact typesalso require low friction, and a lubricant is always required betweenthe sliding materials to prevent seizing and galling

The materials used range from pure metals and alloys to

compos-ites, including those made by powder-metallurgy methods Copper is

widely used but requires protection from oxidation and corrosion,such as by immersion in oil, coating, or vacuum sealing

Copper-tungsten alloys or mixtures of copper-graphite increase

resistance to arcing and sticking, and some copper alloys providegreater hardness, thus greater wear resistance, and better spring

characteristics Silver is more oxidation-resistant in air and, pure or

alloyed, is the most widely used metal for make-and-break contacts

for application at currents to 600 A Silver-copper alloys provide

greater hardness but less conductivity and oxidation resistance;

silver-cadmium alloys increase resistance to arc erosion and

stick-ing; and silver-platinum alloys, silver-palladium alloys, and

silver-gold alloys increase hardness, wear resistance, and oxidation

resistance All alloying elements, however, decrease conductivity

Gold has outstanding oxidation and sulfidation resistance but, being

soft and prone to wear and arc erosion, is limited to low-current

(0.5-A maximum) applications To enhance these properties, gold alloys, such as gold-silver, gold-copper, gold-silver-platinum,

gold-silver-nickel, and gold-copper-platinum-silver, are more

commonly used Platinum and palladium are also used for contacts

but, again, in alloy form more than as pure metals Among the most

common ones are platinum-iridium, platinu ruthenium, platinum

palladium-ruthenium, palladium-ruthenium, palladium-copper,

and palladium-silver A palladium-silver-platinum-gold alloy for

brushes and sliding contacts is noted for its exceptional modulus of

elas-ticity and high proportional limit Aluminum, tungsten, and

molyb-denum are also used for electrical contacts but mainly in composite

form Aluminum used for contacts provides an electrical conductivity ofabout 60% that of copper, but is prone to oxidation and thus clad orplated with silver, tin, or copper The refractory metals, though providingexcellent resistance to wear and arc erosion, are poor conductors and oxi-dize readily

The principal metals made in composite form by PM methods are

the refractory metals, including those in carbide form, and

copper-base and silver-copper-base metals The refractory metals, notably tungsten andmolybdenum or their carbides, usually serve as a base for infiltratingwith copper or silver, thus combining electrical conductivity and resis-

tance to wear and arc erosion in a single material Many such

compos-ites are common, including tungsten-copper, tungsten-silver,

t u n g s t e n c a r b i d e - s i l v e r, t u n g s t e n c a r b i d e - c o p p e r, tungsten-graphite-silver, and molybdenum-silver The

amount of conductive metal may exceed or be less than that of therefractory metal or refractory-metal carbide A common silver com-

posite is silver-cadmium oxide, which, for a given amount of

sil-ver, provides greater conductivity than a silver-cadmium alloy aswell as greater hardness and resistance to sticking Others include

graphite, nickel, and iron The

silver-graphite composites are used mainly for sliding or brush contacts

ELECTRICAL INSULATORS. Any materials that retard the flow of tricity and are used to prevent the passage or escape of electric cur-rent from conductors No materials are absolute nonconductors; thoserating lowest on the scale of conductivity are therefore the best insu-lators An important requirement of a good insulator is that it notabsorb moisture which would lower its resistivity Glass and porcelainare the most common line insulators because of low cost Pure silicaglass has an average dielectric strength of 500 V/mil (20  106 V/m),and glass-bonded mica about 450 V/mil (17.7  106 V/m), while ordi-nary porcelain may be as low as 200 V/mil (8  106V/m), and steatiteabout 240 V/mil (9.4  106 V/m) Slate, steatite, and stone slabs arestill used for panelboards, but now a great variety of insulatingboards are made by compressing glass fibers, quartz, or minerals withbinders, or standard laminated plastics of good dielectric strength

elec-may be used Vulcoid, of Budd Co., is typical For slots and

separa-tors, natural mica is still valued because of its heat resistance, butbecause of the irregular quality of natural mica and the difficulty ofhandling the small pieces, it has been largely replaced by syntheticmica paper, polyester sheet, or impregnated papers or fabrics The

impregnated fish paper called Armite comes in thicknesses down to

0.004 in (0.010 cm) and has a dielectric strength of 500 V/mil (20 

heat resistance, from Class O insulation, for temperatures to 195°F (90°C), to Class C insulation, for temperatures above 355°F (179°C).

Insulating oils are mineral oils of high dielectric strength and

high flash point employed in circuit breakers, switches, ers, and other electrical apparatus An oil with a flash point of285°F (140°C) and fire point of 310°F (154°C) is considered safe Aclean, well-refined oil will have high dielectric strength, but thepresence of as low as 0.01% water will reduce the dielectricstrength drastically The insulating oils, therefore, cannot bestored for long periods because of the danger of absorbing mois-ture Impurities such as acids or alkalies also detract from thestrength of the oil Since insulating oils are used for cooling as well

transform-as insulating, the viscosity should be low enough for free

circula-tion, and they should not gum Askarel is an ASTM designation for insulating fluids which give out only nonflammable gases if

decomposed by an electric arc They are usually chlorinated matic hydrocarbons such as trichlorobenzene (TCB), but fluori-nated hydrocarbons are also used They have high dielectricstrength, and a dielectric constant below 2 Askarel also refers to

aro-dielectric fluids containing polychlorinated bi-phenyls (PCBs),

which had been widely used in transformers These fluids, whichmay contain as much as 50% PCBs, have been replaced because of

environmental concerns regarding PCBs Insulating gases are

used to replace air in closed areas to insulate high-voltage ment Sulfur hexafluoride for this purpose has a dielectric strength2.35 times that of air The insulating oil, fluids, and gases are gen-

equip-erally referred to as dielectrics, although this term embraces any

insulator

Insulation porcelain, or electrical porcelain, is not usually an

ordinary porcelain except for common line insulators For such uses

as spark plugs they may be molded silica, and for electronic tion they may be molded steatite or specially compounded ceramics,

insula-more properly called ceramic insulators Insulation porcelains

com-pounded with varying percentages of zirconia and beryllia have acrystalline structure and good dielectric and mechanical strengths attemperatures as high as 2000°F (1093°C) These porcelains may have

some magnesia, but are free of silica However, zircon porcelain is

made from zirconium silicate, and the molded and fired ceramic is

equal to high-grade steatite for high-frequency insulation Vitrolain,

of Star Porcelain Co., is an electrical porcelain of high strength and

density with porosity of only 0.25% Thyrite, of General Electric Co.,

is a porcelain that possesses the property of being an insulator at lowpotentials and a conductor at high potentials It is used for lightning

arresters The German Hartporzellan, or hard porcelains, are

cially compounded ceramics having good resistance to thermal shock.

The material called Nolex by the Naval Surface Weapons Center

(NSWC) is made by hot-molding finely powdered synthetic fluorinemica The molded parts are practically pure mica They can bemachined, have high-dimensional precision because they need no fur-ther heat treatment, and have high dielectric strength Beryllia is avalued insulator for encapsulation coatings on heat-generating elec-tronic devices as it has both high electrical resistivity and high heatconductivity

Most ceramics are electrical insulators and are used widely for

insulation of electric power lines The applications range from tural power insulators to electronic packaging and substrates Ofparticular interest is the use of ceramics as substrates The ceram-ics serve as the structural and insulating base on which electroniccomponents are deposited or attached The requirement for goodsurface finish has led to the development of fine-grained aluminamaterial that can be prepared with a very good finish The require-ment for high thermal conductivity in some applications has led to

struc-the use of beryllia, high-purity alumina, and more recently,

alu-minum nitride as substrate materials Other materials are silicon carbide doped with beryllia to give electrical insulation and glass- ceramics which can easily be produced in the complex shapes often

needed They can also be produced with a tailored thermal

expan-sion coefficient multilayer ceramic (MLC) substrate for

high-speed computer processing modules

ELECTRICAL-RESISTANCE METALS AND ALLOYS. This major family of

metals, including alloys as well as pure metals, includes resistance

alloys used in controls and instruments to measure or regulate

electri-cal performance, heating alloys used to generate heat, and

thermo-stat metals used to convert heat to mechanical energy There are

seven types of electrical-resistance alloys: (1) radio alloys, which tain 78 to 98% copper with the balance nickel; (2) manganins, 87%

con-copper and 13 manganese or 83 to 85 con-copper, 10 to 13 manganese, and

4 nickel; (3) constantans, 55 to 57% copper and 43 to 45 nickel; (4) nickel-chromium-aluminum alloys, 72 to 75% nickel,

20 chromium, 3 aluminum, and either 5 manganese or 2 copper, iron,

or manganese; (5) iron-chromium-aluminum alloys, 73 to 81% iron,

15 to 22 chromium, and 4 to 5.5 aluminum; (6) various other alloys,

mostly nickel-base alloys, some of which contain substantial

amounts of chromium or iron, chromium and iron, chromium and silicon, and, in some cases, manganese and aluminum; and (7) pure

metals, notably aluminum, copper, iron, nickel, precious metals, and refractory metals.

Key characteristics of resistance alloys are uniform resistivity, ble resistance, reproducible temperature coefficients of resistance,and low thermoelectric potential compared to copper Less critical,but also important, are the coefficient of thermal expansion; strengthand ductility; corrosion resistance; and joinability to dissimilar met-als by welding, brazing, or soldering Heating alloys require high heatresistance, including resistance to oxidation and creep in particularenvironments, such as furnaces, in which they are widely used; highelectrical resistivity; and reproducible temperature coefficients ofresistance Also desirable are high emissivity, low coefficients of ther-mal expansion, and low modulus to minimize thermal fatigue,strength, and resistance to thermal shock, and ductility for fabricabil-ity Thermostat metals, two or more bonded materials of which onemay be nonmetallic, are chosen based on different electrical resistivi-ties and thermal expansivities so that applied heat can be converted

48 (80); and tungsten, 33 (55) The radio alloys are in the 30 to 180 (50

to 300) range, the manganins 228 to 289 (380 to 480), the constantans

295 to 300 (490 to 500), and most of the nickel-chromium-aluminum,iron-chromium-aluminum, and various other alloys are in the 610 to

872 (1,015 to 1,450) range Temperature coefficients of resistance inparts per million per degree Fahrenheit (Celsius) range from ±10 to

±15 at 59 to 113°F (15 to 45°C) for the manganins to +6,000 at 68 to95°F (20 to 35°C) for pure nickel Thermoelectric potentials versuscopper in the
V/°F range from 43 to 77 to 221°F (25 to 105°C) forthe 57 copper–43 nickel constantan to +12.2 at 32 to 167°F (0 to 75°C)for pure iron The refractory metals have the lowest coefficients ofthermal expansion, aluminum the highest, and most of the alloys areintermediate Tensile strength and ductility also range widely depend-ing on the alloy or metal Maximum operating temperatures in air forthe commonly used resistance-heating alloys range from 1700°F(927°C) for 43.5 Fe–35 Ni–20 Cr–1.5 Si alloy to 2505°F (1374°C) for

72.5 Fe–22 Cr–5.5 Al For platinum, this temperature is 2750°F

(1510°C) The refractory metals are suitable for still higher

tempera-tures in vacuum and, in the case of molybdenum and tungsten, in

select environments

Electrical-resistance alloys are mainly wire products, and the alloyshave been known by a multitude of trade names The standard alloyfor electrical-resistance wire for heaters and electrical appliances is

nickel-chromium, but nickel-manganese and other alloys are

used For consumer products made in large quantities, cost and therelative scarcity of the alloying elements are important considera-tions For high-temperature furnaces, tungsten, molybdenum, andalloys of the more expensive high-melting metals are employed Themuch-used alloy with 80% nickel and 20 chromium resists scalingand oxidation to 2150°F (1177°C), but it is subject to an intergranular

corrosion, known as green rot, which may occur in chromium above

1500°F (816°C) unless modified with other elements The 80–20 alloyhas a resistivity of 354  108  ft (108  108   m) The tensilestrength of the annealed wire is 100,000 lb/in2 (689 MPa), with elon-gation of 35%, and the hardness is Rockwell B 80 The specific gravity

is 8.412 In many appliances, high elongation is undesirable because

it causes the wire to sag

In times of nickel stringency, or for cost reduction, various

nickel-chromium-iron alloys are used An alloy of 60% nickel, 16

chromium, and 24 iron has a resistivity of 675  with oxidation

resistance to 1950°F (1066°C) Tophet C is this alloy The alloy with

30% nickel, 20 chromium, and 50 iron is resistant to 1560°F (849°C).The resistivity of the low-nickel, chromium-iron alloys is high, andthe heat resistance is ample for some types of appliances, but the

strength is lower, with a tendency for the hot wire to sag Cromel

AA, of Hoskins Mfg Corp., is an 80–20 nickel-chromium alloy for

continuous service to 2150°F (1127°C) It is modified with smallamounts of cobalt, manganese, columbium, silicon, and iron, thecolumbium stabilizing the chromium to prevent green rot It is alsoresistant to carbon pickup which tends to make the chromium-ironalloys brittle The resistance of the wire is 381  108  ft (116 

108  m)

The chromium-aluminum-iron alloys have high resistivity and

high oxidation resistance, but have a tendency to become brittle

Hoskins alloy 870 contains 22.5% chromium, 5.5 aluminum, 0.5

sil-icon, 0.10 carbon, and the balance iron The resistivity is 466  108

  ft (142  108   m) It is used as wire or ribbon in furnaces to

2350°F (1288°C) The Kanthal alloys marketed as wire and ribbon

by Kanthal Corp have 20 to 25% chromium with some cobalt and

aluminum, and the balance iron Kanthal A, with 5% aluminum,

will withstand temperatures to 2370°F (1299°C), has a resistivity of

456 108  ft (139  108  m), and is resistant to sulfuric acid.The tensile strength is 118,000 lb/in2(813 MPa) with elongation of 12

to 16% Kanthal A-1, for furnaces, has a resistance of 872  and an

operating temperature to 2505°F (1373°C) The Nikrothal alloys of

this company are nickel-base modifications of Kanthal They havehigher tensile strength, up to 200,000 lb/in2 (1,378 MPa), to permit

rapid winding of tape without breakage Nikrothal 6 has 60% nickel, 15 chromium, and 25 iron Heating tape, of Rogers Corp.,

designed for heating rocket batteries, is also used for panel heatingand is operable at continuous temperatures up to 250°F (121°C) Ithas three flat wires of copper-nickel alloy encapsulated in Mylar tape0.008 in (0.020 cm) thick and 0.375 in (0.953 cm) wide in lengths to

250 ft (76 m) The rating is 2 W/ft (6.6 W/m), and the dielectricstrength is 2,400 V

A series of alloys of Westinghouse Electric Corp., called Hirox

alloys, contain 6 to 10% aluminum, 3 to 9 chromium, up to 4

man-ganese, with the balance iron except for small additions of boron andzirconium to reduce the size of the aluminum-iron grains and refinethe structure The alloy with 9% aluminum and 9 chromium has aresistivity of 850  and a tensile strength of 118,000 lb/in2(813 MPa)

At 1300°F (704°C) the tensile strength is 15,000 lb/in2(103 MPa) withelongation of 94% Wire will give continuous service in air at 2350°F(1288°C) without failure

Resistance alloys are generally specified for specific uses ratherthan by composition Controlled resistivity over a temperature rangeinstead of high heat resistance is desired for instrument use, while adefinite coefficient of expansion is required for spark-plug wire andother uses where the wire is embedded In some cases, good heat

resistance with selected low resistivity is desired Oxalloy 28, of

GTE Corp., is copper wire clad with 28% by weight of iron alloy It withstands continuous service at 1300°F (704°C) Theresistivity at 1100°F (593°C) is 28  108   ft (8.6  108   m)

chromium-Neyoro G, of J M Ney Co., used for fine resistance wire in

poten-tiometers and electronic applications where high cost is not a factor,has a high gold content with platinum, silver, and copper The drawnwire has a tensile strength of 185,000 lb/in2 (1,275 MPa) and highcorrosion resistance

Copper-manganese alloys have high resistivity, an alloy with 96

to 98% manganese having a resistance of more than 16,400
/in3(1,000
/cm3) But when the manganese content is high, they arebrittle and difficult to make into wire Addition of nickel makes themductile, but lowers resistivity A typical alloy contains 35% man-ganese, 35 nickel, and 30 copper A resistance alloy developed by the

National Bureau of Standards, called Therlo, contains 85% copper, 9.5 manganese, and 5.5 aluminum Fecraloy has 15% chromium,

5 aluminum, and the balance iron It is for temperatures to 1400°F

(760°C) Sparkaloy is a spark-plug wire and is a manganese-nickel

alloy The spark-plug wire of Hoskins Mfg Co., called Hoskins alloy

667, contains 4% manganese, 1 silicon, and the balance nickel The

resistance is 82  108   ft (25  108  m), specific gravity 8.4,and coefficient of expansion 15.1  106/°F (27  106/K) Manganin

contains 80 to 85% copper, 2 to 5 nickel, and 12 to 15 manganese Ithas a tensile strength of 70,000 lb/in2 (482 MPa) and a resistance of

157 108  ft (48  108  m) It is used for coils and shunt wires

in electrical instruments and in sheet form for instrument springs

Tophet A is a standard 80–20 nickel-chromium alloy The tensile

strength is 120,000 lb/in2 (827 MPa) and resistance 354  108  ft(108  108   m) Electrical-resistance alloys, developed by IncoAlloys International, contain 60 to 80% nickel plus chromium andiron They are used for heater elements, resistors, rheostats, resis-tance thermometers, and in potentiometers

Calorite, of General Electric Co., has 65% nickel, 8 manganese, 12

chromium, and 15 iron Excello metal contains 85% nickel, 14

chromium, and 0.5 each manganese and iron It is used in electric

heaters for temperatures up to 2000°F (1093°C) Alumel, of Hoskins

Mfg Co., intended for temperatures up to 2282°F (1250°C), has 94%nickel, 2.5 manganese, 0.5 iron, and small amounts of other elements

Calido, of Driver-Harris Co., contains 59% nickel, 16 chromium, and

25 iron Nichrome V, of the same company, is the 80–20 alloy.

Nichrome S contains 25% nickel, 17 chromium, and 2.5 silicon It is

marketed in sheet form for temperatures up to 1800°F (982°C) Comet

metal, of the same company, used for rheostats, contains 30% nickel, 5

chromium, and the balance iron It has high strength, up to 160,000lb/in2(1,103 MPa), and a resistivity of 570  The Driver-Harris resis-

tance alloy known as Karma contains 20% chromium,

3 iron, 3 aluminum, 0.30 silicon, 0.15 manganese, 0.06 carbon, and thebalance nickel Its melting point is 2552°F (1400°C), its resistivity

800, and the annealed wire has a tensile strength of 130,000 lb/in2

(896 MPa) with elongation 25% Hytemco, of the same company, is

an iron-nickel alloy used for low-temperature wire The resistance

is 6.6  108  ft (2.0  108  m) Magno is a 95% nickel, 5 ganese alloy of the same company; Climax metal has 74% iron, 25

man-nickel, and 1 manganese

ELECTRORHEOLOGICAL (ER) FLUIDS. Suspensions of fine particles,usually polymers, in nonconducting oils or other liquids When anelectric current is passed through them, they turn from liquid to gel-like solids or vice versa in 0.001 to 0.0001 s With the amount ofapplied voltage governing the degree of solidity, the fluid itself canperform various control functions, such as damping shock and vibra-

tion Particles include aluminosilicate zeolites and polyacene

quinones The most common fluids are silicone oils, gasoline, and kerosene Advanced Fluid Systems, Ltd., of England, supplies a 20

to 40% solution of lithium-polymethacrylate particles in

chlori-nated paraffins, silicone, or mineral oil depending on propertyrequirements ER Fluid Development Ltd., of England, has a series ofERFs that used crosslinked lithium polymethacrylate particles in

low-molecular-weight fluorosilicone fluids Asahi Chemical Industries, of Japan, has developed specially plated and coated nylon

spheres in dimethyl silicone.

ELEMI. A soft, sticky, opaque resin with a pleasant odor, obtained

from the pili tree, Canarium luzonicum, of the Philippines and

employed for giving body and elasticity to lacquers and in

litho-graphic inks In medicine it is used in ointments It contains

dipen-tene, C10H18, which is called limonene from its lemonlike odor, and

is known as cajeputene when obtained from cajeput Limonene

dioxide, or dipentene dioxide, a colorless liquid of composition

C10H12O2, is a valuable synthetic chemical for making epoxy resinsand for cross-linking acrylic and other resins Elemi also contains a

related terpinene oil, phellandrene Substitute elemi resins are

obtained from various trees of the family Burseraceae of tropical

Africa and America The pili trees are hacked or stripped, and theresin collects on the bark, a tree yielding about 5 lb (2.3 kg) per year

West Indian elemi is from the tree Dacryodes hexandra of the West

Indies Nauli gum is elemi from the tree C commune of the

Solomons Elemi oil, obtained by distilling elemi, is a colorless liquid

of specific gravity 0.87 to 0.91, used in perfumes and in medicines Ithas an aniselike odor

ELKSKIN. The commercial name for soft, pliable, and durableleather made from the bundled rawhides known as kips, or fromovergrown calf by a special tanning process and impregnation withoils It is used chiefly for children’s shoe uppers and for pocket-

books A heavier elkskin, or elk leather, for sport shoes and boots,

is made from cowhides by the same treatment Elkskin, like

chamois, dries out to its original softness after wetting Smoked

elk is elk leather dyed cream-colored to imitate the original leather

of elks, which was smoked over a wood fire

ELM. The wood of several species of the elm tree, of the eastern United

States and Canada and northern Europe The wood of the American

elm, or white elm, Ulmus americana, has a fine grain, has a density of

about 40 lb/ft3(641 kg/m3), is hard and tough, and is whitish brown It is

the best known commercially of the six species grown in the UnitedStates The American elm is not a forest tree, but is grown as a shadeand ornamental tree It does not grow in the mountains The trees some-times reach a diameter of 6 ft (1.8 m) and a height of 100 ft (30 m) Thetough, durable wood is valued for ax handles and for parts requiring acombination of strength, bending qualities, and ability to withstandrough use The wood of this tree, and of the rock elm, was formerly usedfor superstructures of naval ships because it did not sharp-splinter likeoak It was also the favorite wood for hubs and spokes of heavy wagon

wheels Rock elm, or hickory elm, U thomasii, is also native to the

United States and Canada It has a very fine, close grain and is slightly

heavier It is sometimes called cork elm, although this name applies to

the wahoo, or winged elm, U alata, of the southeastern states,

because of the corky appearance of the twigs The winged elm is grown

as a shade tree, but the wood was valued for vehicle parts English elm,

U procera, has a straight trunk and rounded crown more like the oaks.

Chinese elm, U parvifolia, has small leaves and is very resistant to

dis-ease Slippery elm is a smaller forest tree, U fulva, of the northeastern

United States Considerable lumber came from this tree under the name

red elm The inner bark of the tree is mucilaginous with a sweet taste

and characteristic odor It was used by the Indians as a chewing gumand as a poultice for skin infections The dried and powdered bark is now

used in medicine for skin infections and for the throat It contains ulmic

acid, or geic acid, C20H14O6

EMERY. A fine-grained, impure variety of the mineral corundum, withthe fine crystals of aluminum oxide embedded in a matrix of iron oxide

It usually contains only 55 to 75% Al2O3 The specific gravity is 3.7 to4.3 and Mohs hardness about 8 It occurs as a dark-brown, granularmassive mineral It is used as an abrasive either ground into powder or

in blocks and wheels In the natural block material, the grains areirregular, giving a varying grinding performance The grains aregraded in sizes from 220 mesh, the finest, to 20 mesh, the coarsest

Emery paper and cloth are usually graded from 24 to 120 mesh, and

the grains are glued to one side of 9- by 11-in (23- by 28-cm) sheets

Flour of emery is the finest powder, usually dust from the crushing Emery cake as made for buffing and polishing is not likely to be made

of emery but a graded combination of aluminum oxide and iron oxide,with a higher percentage of the hard aluminum oxide for buffing, andhigher iron oxide for polishing It is furnished in various grades of fine-ness, with grains of 120 to 200 mesh, or flour sizes, F, FF, and FFF.Emery takes its name from Cape Emery, on the Island of Naxos

EMULSIFYING AGENTS. Materials used to aid in the mixing of uids that are not soluble in one another, or to stabilize the suspen-sion of nonliquid materials in a liquid in which the nonliquid is notsoluble The suspension of droplets of one liquid in another liquid in

liq-which the first liquid is not soluble is called an emulsion The

emulsion of oil and water, used in machine shops as a cutting cant and work coolant, may be made with soap as the emulsifyingagent The emulsifying agent protects droplets of the dispersedmedium from uniting and thus separating out The oil itself may betreated so that it is self-emulsifying Sulfonated oils contain strongnegatively charged ester sulfate groups in the molecule and do notreact and conglomerate with the molecules of a weakly charged liq-uid They will thus form emulsions with water without any otheragent

lubri-In emulsions of a powder in a liquid, an emulsifying agent called a

protective colloid may be used This is usually a material of high

molecular weight such as gelatin, and such materials form a tive film around each particle of the contained powder A photographic

protec-emulsion is a suspension of finely divided silver halide grains in

gelatin The gelatin serves as a binder, protective colloid, and 3 tizer for the silver halide The emulsion consists of 35 to 40% silverhalide, 60 to 65 gelatin, with small amounts of stabilizers, antifog-

sensi-gers, and hardeners Saponin and starches are commonly used thus

as suspending agents For the suspension of drug materials in pharmaceutical mixtures, gum arabic or tragacanth may be used.

Starches, egg albumin, and proteins are common emulsifying agents

for food preparation Alginates are among the best suspending

agents for a wide range of emulsions because of the numerousrepelling charges in the high molecular weight and the irregular con-figuration of the chain, but when added to protein-containing liquidssuch as many foodstuffs, the similar conditions of the algin and theprotein molecules cause a neutralization reaction and a precipitation

of the agglomerated particles Suspending agents generally increasethe viscosity of the liquid, and with high concentrations of some gums

or resins, the water molecules may be completely encased in the resinlattice as a semisolid or water-filled plastic

Sucrose esters, used as emulsifiers for foods, cosmetics, and drugs,

are made from sugar and palmitic, lauric, or other fatty acids Themonoesters are soluble in water and in alcohol, and the diesters are oil-

soluble Sorbester, of Howards of Ilford, Ltd., for emulsifying fatty stuffs, is a diester of sucrose Sucrodet D-600, of Millmaster Chemical

food-Co is a white, tasteless, and odorless powder made from sugar and

palmitic acid Myrj 45, of Atlas Chemical, is polyoxyethylene stearate.

Propylene laurate is a light, high-boiling-point liquid that is

emulsifying in water and is employed in foodstuffs and pharmaceuticals

to stabilize the mixtures The sodium salt of ursolic acid is a strong

emulsifying agent for oil-in-water mixtures The acid is a complex pene obtained from the skins of the cranberry An ionic emulsifier has

triter-an orgtriter-anic lipophilic group (L) triter-and a hydrophilic group (H), the baltriter-ancebetween the two characterizing such classes of emulsifiers and surfac-

tants An anionic emulsifier is triethanol stearate, and a nonionic one

is P.E.G 300 distearate; both emulsify oil in water Cold-cream sions are water in oil; the emulsifier is sodium cerotate produced by reacting borax with cerotic acid The latter occurs freely in beeswax.

emul-Some solid materials may be suspended indefinitely in liquids ifground to such a fineness that the electronegative mutually

repelling force, or zeta potential, of the particles is greater than

the force of gravity Silica, for example, has only a feeble ativity, and if the particles are below about 39
in (1
m), they willgive a permanent suspension in water These finely ground solids

electroneg-are used as thickening agents for paints and coatings Bentonite

is thus used in adhesives and paints and for imparting ian rheologies to drilling muds Thickening agents may add otherproperties such as better adhesion or strengthening the film Somelong-chain chemicals used as emulsifying agents in cutting oils also

nonnewton-give antirust properties Thickening agent ASE-95, of Rohm &

Haas Co., has a powerful thickening action on water-base emulsionswhich can be halted at any desired viscosity by neutralizing theacidity It is an acrylic copolymer of 20% solids containing anorganic acid with a pH of 3 When added to the emulsion to be thick-ened, the solids dissolve in minute particles, and the process isstopped at the desired viscosity by adding an alkali

ENAMEL. A coating which upon hardening has an enameled or

glossy face Pottery enamels, ceramic enamels, or ceramic

coatings, and vitreous enamels are composed chiefly of quartz,

feldspar, clay, soda, and borax, with saltpeter or borax as fluxes.The quartz supplies the silica, and such enamels are fusibleglasses In acid-resisting enamels, alkali earths may be usedinstead of borates To make enamels opaque, opacifiers are used.They may be tin oxide for white enamel, cobalt oxide for blue, orplatinum oxide for gray Enamel-making materials are prepared in

the form of a powder which is called frit The frit-making

ture is about 2400°F (1316°C), but the enamel application tures are from 1400 to 1600°F (760 to 871°C) Each succeeding coathas a lower melting point than the one before it, so as not todestroy the preceding coat It must also have about the same coeffi-cient of expansion as the metal to prevent cracking Enamels for

aluminum usually have a high proportion of lead oxide to lower themelting point, and enamels for magnesium may be based onlithium oxide Some enamels for low-melting-point metals have theceramic frit bonded to the metal with monoaluminum phosphate attemperatures as low as 400°F (204°C).

The mineral oxide coatings fused to metals are often called

porce-lain enamels, but they are not porceporce-lain, and the term vitreous enamel is preferred in the industry, although ceramic-lined tanks

and pipe are very often referred to as glass-lined steel The

composi-tion varies greatly, one company having more than 3,000 formulas.Vitreous enameled metals are used for cooking utensils, signs, chemi-cal tanks and piping, clock and instrument dials, and siding and roof-ing Ground coats are usually no more than 0.004 in (0.010 cm) thick,and cover coats may be 0.003 to 0.008 in (0.006 to 0.020 cm) thick.The hardness ranges from Knoop 150 to 500 Thick coatings on thinmetals are fragile, but thin coatings on heavy metals are flexibleenough to be bent Standard porcelain-type enamel has a smooth,glossy surface with a light reflectance of at least 65% in the whitecolor, but pebbly surfaces that break up the reflected image may beused for architectural applications

High-temperature coatings may contain a very high percentage ofzirconium and will withstand temperatures to 1650°F (899°C)

Refractory enamels, for coating superalloys to protect against the

corrosion of hot gases to 2500°F (1371°C), may be made with dard ceramic frits to which is added boron nitride with a lithiumchromate or fluoride flux Blue undercoats containing cobalt are gen-erally used to obtain high adhesion on iron and steel, but some of the

stan-enameling steels do not require an undercoat, especially when a

specially compounded frit or special flux is used When sodium

alu-minum silicate, Na2O Al2O3 6SiO  xH2O, is used instead of borax,

a white finish is produced without a ground coat Mirac is a white

enamel which gives good adhesion directly to steel Enamels ing titanium oxide will adhere well to steels alloyed with a small

contain-amount of titanium Ti-Namel, of Inland Steel Co., is an enameling

steel containing titanium

Many trade names are applied to vitreous enamels and to enameled

metals Vitric steel is an enameled corrugated sheet steel for struction Majolica is an old name for marblelike enamels made by mixing enamels of different colors, but mottled graywear is made

con-with cobalt oxide on steel that has a controlled misting on the surface

Cloisonné enamel is an ancient decorative enamel produced by

sol-dering thin strips of gold on the base metal to form cells into which thecolored enamel is pressed and fused into place It requires costly handmethods and is now imitated in synthetic plastics under names such

as Enameloid.

The word enamel in the paint industry refers to glossy varnishes

with pigments or to paints of oxide or sulfate pigments mixed with nish to give a glossy face They vary widely in composition, in color andappearance, and in properties As a class, enamels are hard and toughand offer good mar and abrasion resistance They can be formulated toresist attack by the most commonly encountered chemical agents andcorrosive atmospheres Because of their wide range of useful proper-ties, enamels are one of the most widely used organic finishes in indus-

var-try and are especially used as household appliance finishes Japan is a

name applied to black baking enamels Japan consists of a pigment, agum, a drying oil, and a reducer, the same as any oil enamel It isalways baked, which drives off the solvent and fuses the gum into a uni-form vitreous layer Japans have now been replaced by synthetic bakingfinishes The modified phenolmelamine and alkyd-melamine syntheticresins produce tough and resistant enamel coatings Quick-drying

enamels are the cellulose lacquers with pigments Fibrous enamel,

used for painting roofs, is an asphalt solution in which asbestos fibershave been incorporated When of heavy consistency and used for caulk-

ing metal roofs, it is called roof putty.

EPOXY RESINS. A class of synthetic resins characterized by having in

the molecule a highly reactive oxirane ring of triangular

configura-tion consisting of an oxygen atom bonded to two adjoining and bondedcarbon atoms They are usually made by the reaction of epichlorohy-drin with phenol compounds, but epoxidation is also done by the oxi-dation of a carbon-to-carbon double bond with an organic peracid such

as peracetic acid Epichlorohydrin is produced from allyl chloride

and is a colorless liquid with a chlorine atom and an epoxide ring

The dipoxy resins made by the oxidation of olefins with peracetic

acid have higher heat resistance than those made with bisphenol

Epoxidation is not limited to the making of plastic resins, and

epoxi-dized oils, usually epoxiepoxi-dized with peracetic acid, are used as paint

oils and as plasticizers for vinyl resins

Epoxy resins are generally more costly than many other mosetting resins, but, because of their combinations of high mechan-ical and electrical properties, they are important, especially for suchuses as adhesives, chemically resistant coatings, and encapsulation

ther-of electronic units The resins are thermosetting and inert For sulation, they cast easily with little shrinkage They have very highadhesion to metals and nonmetals, heat resistance from 350 to500°F (177 to 260°C), dielectric strength to 550 V/mil (22 V/m), andhardness to Rockwell M 110 The tensile strength may be up to12,000 lb/in2 (83 MPa), with elongation to 2 to 5%, but someresilient encapsulating resins are made with elongation to 150%

with lower tensile strengths The resins have high resistance tocommon solvents, oils, and chemicals.

An unlimited variety of epoxy resins are possible by varying thebasic reactions with different chemicals or different catalysts, orboth, by combination with other resins, or by cross-linking withorganic acids, amines, and other agents To reduce cost when used

as laminating adhesives, they may be blended with furfural resins,giving adhesives of high strength and high chemical resistance.Blends with polyamides have high dielectric strength, mold well,and are used for encapsulating electrical components By using apolyamide curing agent an epoxy can be made water-emulsifiablefor use in water-based paints An epoxy resin with 19% bromine inthe molecule is flame-resistant Another grade, with 49% bromine,

is a semisolid, used for heat-resistant adhesives and coatings

Epoxidized polyolefins have five or more reactive epoxy groups

along each molecule of the chain instead of the usual two terminalepoxy groups on each molecule With dibasic acids or anhydridesthey form strong, hard resins of high heat resistance; or resins oflower viscosity are made for laminating and casting Epoxy resinsmade by the reaction of epichlorohydrin with a phenol-formaldehyderesin with an anhydride catalyst have heat distortion points of 570°F(300°C) As an adhesive for laminates, they give very high strength

at elevated temperatures Epoxies can be copolymerized with other

resins Epoxy-acrylate resin, used for glass-fiber laminates,

com-bines the resistance and adhesiveness of the epoxy with the fastcure and strength of the acrylate Epoxy resins can be made withcyclopentyl oxide terminal groups instead of diglycidyl ether Theyield strength at 392°F (200°C) is 18,200 lb/in2(123 MPa), and theyhave a heat deflection temperature of 434°F (223°C) Epoxy resins

can be produced by a reaction of hydantoin with epichlorohydrin.

Hydantoin is a nitrogen-containing heterocyclic compound Theyhave high mechanical properties, good dielectrical characteristics,and ultraviolet light resistance They retain light transmissionproperties after thermal aging of several thousand hours at 302°F(150°C)

Epoxy has been the major matrix material of polymer-matrix

composites for aircraft applications for many years This is

attribut-able to ease of processing (low-pressure, moderate-temperature clave or press curing), good mechanical properties, and low cost Theprincipal reinforcements are fibers of aramid (Kevlar), boron, glass,and graphite In such applications, the composites are used for servicetemperatures up to about 300°F (149°C) In recent years, however,

some aircraft manufacturers have replaced epoxy with

bis-maleimides, which process much as epoxy does and can be used at

service temperatures up to about 350°F (177°C) Prepreg 977, of ICI

Fiberite, is an epoxy toughened with a proprietary thermoplastic tomer so as not to sacrifice compression strength while increasingtoughness Unlike some elastomer-modified grades, the elastomer is

elas-an integral part of the resin so that it unites in the epoxy backbone oncuring Compression-after-impact strength and wet-service tempera-tures range from 47,000 lb/in2(324 MPa) and 180°F (82°C) for 977-1 to30,000 lb/in2 (207 MPa) and 250°F (121°C) for 977-3 Shell Chemical’s

Epon HPT 1077 epoxy is an amine-based compound, which combines

low viscosity with good mechanical properties and chemical and heatresistance At 77°F (25°C), viscosity is about 3,500 cP, one-fourth that

of Epon 828 It also has a glass transition temperature of 500°F (260°C), which is high for a low-viscosity resin PR-500, of 3M, is a

one-part compound that can resist temperatures up to 350°F (177°C).Reinforced with 50% glass fiber, it is used for resin-transfer-moldedvent louvers of auxiliary power units on large commercial aircraft

FR-4 is a halogenated epoxy compound widely used for printed-circuit

boards

Novoloids are fibers containing at least 85%, by weight,

cross-linked novalac epoxies Kynol is a novoloid noted for its

exception-ally high temperature resistance At 1920°F (1049°C) the fiber isvirtually unaffected The fiber also has high dielectric strength andexcellent resistance to all organic solvents and nonoxidizing acids

Shell Chemical’s Epon HPT 1050 epoxy is a novalac compound in

semisolid neat resin form or as a 75% by weight solution in acetone

Epon 861 epoxy is a bisphenol F low-viscosity compound for

resin-transfer molding or use as an adhesive Eposert, of Ciba Geigy, is a line of epoxy syntactic inserts for reinforcing honeycomb.

SynSpand, of Dexter Aerospace, is a line of epoxy-based, expandable

syntactic films

A family of one-component epoxy resins, named Arnox, was

devel-oped by General Electric Co Suitable for compression, transfer,injection molding, filament winding, and pultrusion, they curerapidly at temperatures of 250 to 350°F (121 to 177°C) The compres-sion and transfer-molding grade is a black, mineral-filled compound.The injection-molding grade is a pelletized glass-fiber-reinforcedcompound with a shelf life of 9 to 12 months below 80°F (27°C)

ESSENTIAL OILS. Aromatic oils found in uncombined form in variousparts of plants and employed for flavors, perfumes, disinfectants,

medicines, and stabilizers; for masking undesirable odors; and asraw materials for making other products They are usually the estersupon which the odiferous properties of the plants depend, and theyare called essential oils because of their ease of solubility in alcohol

to form essences They are also called volatile oils, although this

term is sometimes also applied to the light and volatile distillatesfrom petroleum The essential oils are of four general classes: the

pinenes or terpenes of coniferous plants, containing carbon and

hydrogen of the empirical formula C1 0H1 6, such as oil of

turpentine; oxygenated oils containing carbon, hydrogen, and

oxygen, such as oil of cassia; nitrogenated oils containing carbon, hydrogen, oxygen, and nitrogen, such as oil of bitter almonds; sul-

furated oils containing carbon, hydrogen, and sulfur, such as oil of mustard.

Although fixed vegetable oils are obtained by expression, the tial oils are obtained by distilling the buds, flowers, leaves, twigs, or

essen-other parts of the plant Rose oil is found only in the flowers.

Orange oil and lemon oil are from the flowers and the fruits, but

are of different compositions Sweet birch oil and cinnamon oil are from the bark Valerian and calamus are only in the roots, while

sandalwood oil and cedar oil are only in the wood Sometimes the

essential oil is not in the plant, but is developed when the plant is

macerated with water The alpha pinene extracted from turpentine

is used for paints and varnishes because it has a high evaporationrate It is a water-white liquid of pleasant odor boiling at 325°F

(163°C) It is also used in the synthesis of camphor Pinic acid is a

complex carboxycyclobutane acetic acid produced from alpha pinene

Its esters are used for synthetic lubricants Balsams are solid or

semisolid resinous oils and are mixtures of resins with cinnamic orbenzoic acid, or both, with sometimes another volatile oil They areobtained from a variety of trees and are used in antiseptics, perfumes,flavors, and medicine

Some of the essential oils contain alkaloids which have a physiological

effect Wormwood oil, distilled from the dried leaf tops of the perennial

herb Artemisia absinthium, native to southern Europe but also grown in

the United States, is used in medicine for fevers, and for flavoring the

liqueur absinthe The drug santonin, used for worm treatment for

ani-mals, is an alkaloid extracted from the unopened flower heads of the

Levant wormseed, A cina, of the Near East, but wormseed oil, or

Baltimore oil, used for the same purpose, is an essential oil containing

the alkaloid ascoridole It is distilled from the seeds and leaf stems of the

annual plant Chenopodium anthelminticum, grown in Maryland.

ESTERS. Combinations of alcohols with organic acids, which form eral important groups of commercial materials The esters occur natu-rally in vegetable and animal oils and fats as combinations of acidswith the alcohol glycerin The natural fats are usually mixtures ofesters of many acids, coconut oil having no less than 14 acids Stearic,oleic, palmitic, and linoleic acid esters are the common bases for mostvegetable and animal fats, and the esters of the other acids such aslinolenic, capric, and arachidic give the peculiar characteristics of theparticular fat, although the physical characteristics and melting pointsmay be governed by the basic esters Esters occur also in waxes, thevegetable waxes being usually found on the outside of leaves and fruits

sev-to protect them from loss of water The waxes differ from the fats inthat they are combinations of monacids with monohydric, or simple,alcohols, rather than with glycerin They are harder than fats and havehigher melting points Esters of still lower molecular weights are alsowidely distributed in the essential oils of plants where they give thecharacteristic odors and tastes All the esters have the characteristic

formula ArCOOR or RCOOR, where R represents an alkyl group, and

Ar an aryl group, that is, where R is a univalent straight-chain

hydro-carbon having the formula CnH2n1and Ar is a univalent benzene ring

C6H5 In the esters of low molecular weight which make the odors andflavors, the combination of different alcohols with the same acid yieldsoils of different flavor Thus the ester methyl acetate, CH3COOCH3, is

peppermint oil; amyl acetate, CH3COOC5H11, is banana oil; and

isoamyl acetate, CH3COO(CH2)3(CH3)2, is pear oil Esters are used as

solvents, flavors, perfumes, waxes, oils, fats, fatty acids, cals, and in the manufacture of soaps and many chemicals Ester liquidlubricants have good heat and oxidation resistance at high tempera-tures and good fluidity at low temperatures They are widely used injet aircraft

pharmaceuti-The natural esters are recovered by pressing or extraction, and steamdistillation Synthetic esters are prepared by reacting an alcohol with an

organic acid in the presence of a catalyst, such as sulfuric acid or

para-toluenesulfonic acid The product is purified with an azeotrope, such

as benzene or toluene A range of cellulose acetate esters are made by esterification of cellulose with acetic anhydride Cellulose nitrate ester

is obtained by reacting cellulose with nitric acid, cellulose sulfate from

chlorosulfonic acid in pyridine solvent, and cellulose phosphate

from phosphoric acid in molten urea Alkoxysilanes are silicon esters in

which the silicon is connected to an organic group by oxygen

Tetraethoxysilane, a low-molecular-weight compound, is reactive and

is used in binders, resins, and glasses and as a cross-linking agent

Tetrabutoxysilane is more stable and is used in lubricants and

heat-transfer fluids

Ester alcohols are intermediates that require less acid for

esterifi-cation Texanol, of Eastman Chemical Co., has both a hydroxy group

and an ester linkage with the empirical formula C12H24O3 It produces

a wide range of chemicals and compounds with low, 71°F (57°C),pour point

ETCHING MATERIALS. Chemicals, usually acids, employed for ting into, or etching, the surface of metals, glass, or other material

cut-In the metal industries they are called etchants The usual method

of etching is to coat the surface with a wax, asphalt, or other stance not acted upon by the acid; cut the design through with asharp instrument; and then allow the acid to corrode or dissolve theexposed parts For etching steel, a 25% solution of sulfuric acid inwater or a ferric chloride solution may be used For etching stain-less steels, a solution of ferric chloride and hydrochloric acid inwater is used For high-speed steels, brass, or nickel, a mixture ofnitric and hydrochloric acids in water solution is used, or nickelmay be etched with a 45% solution of sulfuric acid Copper may beetched with a solution of chromic acid Brass and nickel may beetched with an acid solution of ferric chloride and potassium chlo-rate For red brasses, deep etching is done with concentrated nitricacid mixed with 10% hydrochloric acid, the latter being added tokeep the tin oxide in solution and thus retain a surface exposed tothe action of the acid For etching aluminum a 9% solution of cop-per chloride in 1% acetic acid, or a 20% solution of ferric chloridemay be used, followed by a wash with strong nitric acid Sodiumhydroxide, ammonium hydroxide, or any alkaline solutions are alsoused for etching aluminum Zinc is preferably etched with weaknitric acid, but requires a frequent renewal of the acid Strong acid

sub-is not used because of the heat generated, which destroys the waxcoating A 5% solution of nitric acid will remove 0.002 in (0.005 cm)

of zinc per minute, compared with the removal of over 0.005 in(0.013 cm) per minute in most metal-etching processes Glass is

etched with hydrofluoric acid or with white acid White acid is a

mixture of hydrofluoric acid and ammonium bifluoride, a whitecrystalline material of composition (NH4)FHF Sodium chlorate may be used as the electrolyte in producing chemical finishes.

The process in which the metal is removed chemically to give thedesired finish as a substitute for mechanical machining is called

chemical machining.

To trace the electrical circuit pathways on silicon chips andprinted-circuit boards, liquid etchants containing acids are used.

Buffered hydrofluoric acid is a selective etchant for silicon

diox-ide in the presence of silicon Ammonium fluordiox-ide is a common

buffer, and its concentrations in the mixture range from 20% to morethan 90 Formulations containing combinations of nitric, acetic,

phosphoric, and sulfuric acids are called mixed-acid etchants.

Ammonium chloride, ammonium persulfate, and cupric ride are used for etching copper printed-circuit boards Ceric ammonium nitrate is suited for etching silicon wafers Dry etch- ing, carried out in the gas phase, employs silicon tetrafluoride

chlo-and carbon tetrafluoride.

ETHER The common name for ethyl ether, or diethyl ether, a

highly volatile, colorless liquid of composition (C2H5)2O made fromethyl alcohol It is used as a solvent for fats, greases, resins, andnitrocellulose, and in medicine as an anesthetic The specific gravity

is 0.720, boiling point 93.6°F (34.2°C), and freezing point 177°F(116°C) Its vapor is heavier than air and is explosive Actually,

ether is a more general term, and an ether is an alkyl oxide with

two alkyl groups joined to an oxygen atom The ethyl ether wouldthus be expressed as C2H5 O  C2H5, and there are many ethers

Butyl ether, (C4H9)2O, has a much higher boiling point, 284°F(140°C); is more stable; and is used as a solvent for gums and resins

Isopropyl ether, (CH3)2CHOCH(CH3)2, is a by-product in the ufacture of isopropyl alcohol from propylene It has a higher boilingpoint than ethyl ether, 156°F (69°C); lower solubility in water; and

man-is often preferred as an extractive solvent Methyl ether, or

dimethyl ether, also known as wood ether, is a colorless gas of

composition (CH3)2O, with a pleasant aromatic odor The boilingpoint is 10.3°F (23.5°C) The specific gravity is 1.562 or, as a liq-uid compressed in cylinders, 0.724 It is used for fuel, as a welding

gas, as a refrigerant, and for vapor-pressure thermometers Hexyl

ether, C6H13OC6H13, has a high boiling point, 439°F (226°C); verylow water solubility; and a specific gravity of 0.7942 It is stable andnot volatile, with a flash point of 170°F (77°C) It is used in foambreakers and in chemical manufacture where anhydrous propertiesare desired A low-boiling-point chemical used as an extractive sol-vent and for plastics because of its stability in alkalies and its high

water solubility is methylal, CH3OCH2OCH3 It is a water-whiteliquid boiling at 108°F (42.3°C) Ether reacts slowly with the oxygen

of air to form highly explosive and poisonous compounds, so thatlong-stored ether is dangerous for use as an anesthetic

ETHYL ALCOHOL Also called methyl carbinol, and ethanol when

made synthetically It is the common beverage alcohol, which when

denatured for nonbeverage purposes is called industrial alcohol.

About 90% of the ethyl alcohol used in the United States is tured Ethyl alcohol is a colorless liquid with a pleasant odor butburning taste The composition is CH3CH2OH, specific gravity 0.79,boiling point 173.3°F (78.5°C), and freezing point 179°F(117.3°C) It mixes with water in all proportions and takes up mois-ture from the air It burns with a bluish flame and high temperature,yielding carbonic acid and water The ignition temperature is 965°F(518°C) It is one of the best solvents and dissolves many organicmaterials such as gums, resins, and essential oils, making solutions

water Methylated spirits is a term first used in England to

desig-nate the excise-free mixture of 90% ethyl alcohol and 10 wood hol for industrial use Denatured ethyl alcohol, made unsuitable forbeverage purposes, may be marketed under trade names such as

alco-Synasol of Union Carbide Solox consists of 100 parts 190-proof

alcohol, 5 ethyl acetate, and 1 gasoline, used for lacquers, fuel, and

as a solvent Neosol, of Shell Chemical Corp., is 190-proof ethyl

alcohol denatured with four parts of a mixture of tertiary butyl hol, methyl isobutyl ketone, and gasoline

alco-Ethyl alcohol is used as a solvent in varnishes, explosives, extracts,perfumes, and pharmaceuticals; as a fuel; as a preserving agent; as

an antifreeze; and for making other chemicals Up to 15% of alcoholcan be used in gasoline motor fuels, called generically by the name

gasohol, without change in carburetion M85, sold in the western

United States, is methanol with 15% alcohol Brazil produces large

quantities of Proalcohol, which contains 22% anhydrous ethanol The German motor fuel Monopolin was a mixture of absolute alcohol

and benzene Ethyl alcohol is classified as a poison when pure, but isemployed as a beverage in many forms In small quantities it is an

exhilarant and narcotic In all countries large amounts of beverage

alcohol are made from starches, grains, and fruits, retaining the

original flavor of the raw material and marketed directly as wines,

whiskies, and brandies But synthetic wines are made by

ferment-ing sugar and addferment-ing vegetable extracts to supply flavor and bouquet

No methyl alcohol or fuel oil is produced in the process Alcohol is duced easily by the fermentation of sugars, molasses, grains, and

starch It is also made cheaply by directly or indirectly hydrating ylene produced by the cracking of petroleum hydrocarbons In Europe

eth-it is also made from the waste liquor of pulp mills by fermentation of

wood sugar Sulfite pulp liquor contains 1.8% fermentable hexose

sugar It is also made directly from wood waste by fermenting thewood sugar molasses Ethanol is concentrated and purified by extrac-tive distillation using an azeotrope, such as benzene

A substitute for ethyl alcohol for solvent purposes and as a rubbing

alcohol is isopropyl alcohol, or isopropanol, a colorless liquid of

composition (CH3)2CHOH, boiling point 180°F (82°C), and produced

by the hydration of propylene from cracked gases It is also used as astabilizer in soluble oils and in drying baths for electroplating

Petrohol is isopropyl alcohol Trichloroethanol, CCl3 CH2OH, is aviscous liquid with an ether odor, boiling at 302°F (150°C) and freez-ing at 55°F (13°C), slightly soluble in water, used for making plasti-cizers and other chemicals The spent grain from alcohol distilleries,

called stillage, is dried and marketed as livestock feed and is a better

feed than the original grain because of the high concentration of

pro-teins and vitamins, with the starch removed The leaf alcohol which

occurs in fruits and many plants is a hexene alcohol It is made thetically for blending in synthetic flavors and for restoring full flavorand fragrance to fruit extracts

syn-ETHYL SILICATE. A colorless liquid of composition (CH2H5)4SiO4, used

as a source of colloidal silica in heat-resistant and acid-resistant ings and for moldings The specific gravity is 0.920 to 0.950 It is a

coat-silicic acid ester, with a normal content of 25% available silica,

although tetraethyl orthosilicate has 27.9% available silica, and

ethyl silicate 40 of Union Carbide has 40% silica The latter is a

brown liquid Water hydrolyzes ethyl silicate to alcohol and silicic

acid, H4SiO2, which dehydrates to an adhesive amorphous silica Formoldings, the ester is mixed with silica powder, and for such products

as bearings, wood flour may be incorporated to absorb and retain thelubricating oil Ethyl silicate solutions are employed for the surfacehardening of sand molds and graphite molds for special casting.Silicic acid ester paints are used to harden and preserve stone,cement, or plaster, and for coating insulating brick They are resis-

tant to heat and to chemical fumes Kieselsol, a German material for

clarifying wine and fruit juices by precipitation of the albumin, is a15% water solution of silicic acid

ETHYLENE Also called ethene A colorless, inflammable gas,

CH2:CH2, produced in the cracking of petroleum Ethylene liquefies at

154.8°F (68.2°C) It was first produced in Holland by dehydrating